JN0-106 Junos OS Fundamentals Practice Question
An administrator notices that after committing a configuration change on a Juniper MX router, the device loses connectivity to the management network. The management interface is part of a dedicated management routing instance. Which of the following is the most likely cause?
⚠ Common exam trap
Test-takers frequently assume a firewall filter or service configuration (like NTP or syslog) is the cause, but the real issue is the removal of the routing instance that provides the logical separation for the management interface.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The routing instance for the management interface was accidentally removed
The management interface is part of a dedicated management routing instance (often named mgmt_junos). If this routing instance is accidentally removed during a commit, the management interface loses its routing context and becomes unreachable, causing loss of connectivity to the management network. This is a common misconfiguration when an administrator modifies routing instance configurations without realizing the management interface depends on it.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
A firewall filter was applied to the management interface that blocks all traffic
Why it's wrong here
A firewall filter that blocks all traffic on the management interface would cause immediate loss of connectivity, but this scenario is unlikely in a well-managed Junos device because the management interface (fxp0/me0) resides in a dedicated routing instance and filters are typically applied to data-plane interfaces only. Accidentally applying such a filter would be a deliberate or obvious change, whereas the symptoms described here are more consistent with a routing instance being removed, which silently eliminates the management route.
- ✗
NTP was configured with an incorrect server address
Why it's wrong here
NTP misconfiguration does not affect connectivity because Network Time Protocol is an application-layer service that only synchronizes the device clock. Even with an incorrect server address, the interface remains operationally up, the routing table is unchanged, and the management interface continues to be reachable. The observed symptom would be a clock skew or NTP sync failure, not a loss of remote access.
- ✗
A syslog server was configured that is unreachable
Why it's wrong here
An unreachable syslog server has no impact on connectivity because syslog is a one-way logging protocol that sends messages over UDP port 514 (or TCP if configured) without requiring a response. The device will simply discard or buffer log messages if the collector is unreachable, but the forwarding plane and routing instances are unaffected. Therefore, the administrator would still be able to manage the device, making this option incorrect.
- ✓
The routing instance for the management interface was accidentally removed
Why this is correct
The management interface (e.g., fxp0 or me0) is bound to a dedicated routing instance, often named mgmt_junos, which contains the management subnet's route. Removing this routing instance from the configuration causes the interface to lose its association with the routing table, effectively eliminating the route to the management network. As a result, remote management traffic cannot be routed to or from the device, even though the interface itself may still be administratively and operationally up. This correctly explains why the administrator loses connectivity after committing the configuration.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This JN0-106 practice question is part of Courseiva's free Juniper Networks certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the JN0-106 exam.